1. Field of the Invention
Embodiments of the present invention relate to a liquid treatment agent coating device, a method of operating the liquid treatment agent coating device, and an image forming system. The liquid treatment agent coating device is for an inkjet printer that forms an image on a recording medium by discharging ink droplets. The liquid treatment agent coating device coats the recording medium with a liquid treatment agent prior to forming the image. The liquid treatment agent is, for example, a blur inhibitor that inhibits an image blur that may occur during recording by the inkjet printer.
2. Description of the Related Art
An inkjet image forming method has rapidly been adopted in recent years owing to an advantageous property that the method is easily enhanced for a method of forming color images, as well as properties that the method is noiseless and has a low running cost. However, when an image is formed by the inkjet image forming method on a recording medium other than dedicated paper, there may be problems in quality of the formed image at an earlier stage, such as blurring, density unevenness, color tone unevenness, and bleed-through. Additionally, there may be problems in robustness of the formed image, such as water resistance and weather resistance. Therefore, some techniques have been proposed to solve these problems.
There is a method for solving these problems. In the method, quality of an image is improved by coating a sheet of paper (as a recording medium) with a liquid treatment agent prior to the ink droplets being adhered to the sheet of paper. The liquid treatment agent functions to condense the ink. As the method of coating the recording medium with the liquid treatment agent, Patent Document 1 (Japanese Patent Laid-Open Application No. H7-156538) discloses a method of coating an entire surface of a recording medium with a liquid treatment agent by using a roller.
FIG. 10 is a schematic configuration diagram of a conventional liquid treatment agent coating device for coating the recording medium with the liquid treatment agent by using the roller. As shown in FIG. 10, the recording medium is wound around a peripheral surface of a platen roller 201 by using a pressing chuck 202. The platen roller 201 is rotationally driven by a driving source such as a motor (not shown).
On the other hand, a liquid treatment agent 205 is reserved in a liquid treatment agent tank 204. The liquid treatment agent 205 is transferred onto a roller surface of a coating roller 208 as a thin film by an agitation-supply roller 206 and conveyance-thinning rollers 207a and 207b. 
The coating roller 208 rotates while being pressed onto the recording medium 203, which has been wound around the platen roller 201 being rotated, thereby coating the surface of the recording medium 203 with the liquid treatment agent 205. When a portion of the recording medium 203, which has been coated with the liquid treatment agent 205, reaches a position facing an inkjet recording head 209, the inkjet recording head 209 discharges ink droplets, thereby performing the recording.
As described, according to the method of coating a recording area of the recording medium 203 with the liquid treatment agent 205 for improving image quality by using the coating roller 208, the recording area can be coated thinly with the liquid treatment agent 205 having a relatively higher viscosity, compared to a method where a recording area is processed by spraying a liquid treatment agent by using a spraying head. Therefore, the method of coating the recording area with the liquid treatment agent 205 has such an advantageous property that an image blur can further be prevented from occurring.
However, for such a conventional liquid treatment agent coating device, it has not been considered that, when the liquid treatment agent has been reserved for a long time in the liquid treatment agent coating device, viscosity of the liquid treatment agent increases due to evaporation of water or an organic solvent in the liquid treatment agent. FIG. 11 is a characteristic diagram showing a relationship between viscosity of a liquid treatment agent and a coating amount of the liquid treatment agent per A4 size recording medium. As is clear from FIG. 11, the coating amount of the liquid treatment agent tends to be increased when the viscosity of the liquid treatment agent is increased.
When the coating amount of the liquid treatment agent is increased, the liquid treatment agent may bleed on the recording medium. Therefore, a friction force between the recording medium and a roller that conveys the recording medium may be lowered. It can be a cause of a conveyance failure of the recording medium. Further, it is possible that the liquid treatment agent is not sufficiently dried. In such a case, it is possible that the formed image is transferred to another recording medium in a post process. Therefore, there are some problems in that the image quality is lowered and that speeding up of the image forming system is prevented.